Generally, axial deformation or misalignment that occurs in a rotational body causes imbalance of the rotational body, which may cause shaft vibration during operation. Excessive shaft vibration causes an abnormality in a bearing part and prevents normal operation. A further progress of the excessive vibration may lead to a break of the shaft. Thus, to prevent such a break, it is important to keep axial deformation or misalignment of the rotational body within an acceptable value.
Rotational bodies covered by the present invention include a gas turbine rotor, and also rotors for a rotary machine such as a steam turbine rotor, a rotor for a compressor, a rotor for a hydraulic turbine, rotors for various pumps, and rotors for various blowers.
A gas turbine rotor will be specifically described by way of example. FIG. 11 shows a general structure of a gas turbine rotor. The gas turbine rotor 1 includes a compressor rotor part 10, a turbine rotor part 20, and an intermediate shaft 25 connecting the rotor parts, and the compressor rotor part 10 and the turbine rotor part 20 are each constituted by disk-shaped rotor disks 50 including blades 11 radially implanted in an outer periphery. The gas turbine rotor 1 has an integral structure in which the rotor disks 50 are placed one next to another in a rotor axis direction and fastened by spindle bolts 30, and opposite ends thereof are supported by bearings S1 and S2.
Axial deformation that occurs in the gas turbine rotor 1 having such a configuration causes shaft vibration. Also, a gap between a front end of each of the blades 11 mounted to the outer periphery of the rotor disk 50 and an outer casing (not shown) is adjusted to be substantially constant in a circumferential direction. An increase in shaft vibration causes interference between the front end of the blade and the casing, which may disable operation. Thus, an axial deformation amount needs to be adjusted at the time of assembling the rotor to be kept within an acceptable value. Also, when the axial deformation exceeds the acceptable value, the axial deformation needs to be corrected.
The axial deformation is corrected by the following procedure. In the configuration of the gas turbine rotor 1 shown in FIG. 11, misalignment data including a misalignment amount and a misalignment angle is calculated for each rotor disk 50 to determine the distribution of axial deformation of the gas turbine rotor 1. An example of the distribution of axial deformation is shown in FIG. 12. The abscissa represents a distance along the rotor from the bearing S1, and the ordinate represents a misalignment amount of each rotor disk 50.
One factor of occurrence of the axial deformation is a nonuniform thickness of the rotor disk 50. Thus, the misalignment amount of the rotor disk 50 sometimes exceeds the acceptable value depending on the way of placing the rotor disks 50 one next to another. In this case, a rotor disk 50 to be corrected is selected from the distribution of axial deformation, joint surfaces between the rotor disks 50 are cut to correct the axial deformation of the gas turbine rotor 1 so as to reduce a contact surface angle (α) between the rotor disks 50 (FIG. 13).
FIG. 13 shows a state where the axial deformation of the gas turbine rotor 1 occurs. FIG. 13 shows the rotor disk 50, a rotor disk joint surface 51, the contact surface angle (α) between adjacent rotor disks 50, and a relationship between a misalignment amount of a rotor core and a radial deflection amount of the rotor disk 50.
The radial deflection amount of the rotor disk 50 is obtained by selecting a plurality of measurement points at circumferentially regular intervals on an outer surface 52 of each rotor disk 50 while rotating the rotor, and measuring a radial displacement amount at each measurement point from a reading of a displacement gauge at the measurement point. Specifically, with reference to a measurement starting point (a displacement amount at the measurement starting point is zero for convenience), a radial displacement amount of the rotor at each measurement point from the measurement starting point is regarded as a deflection amount at each measurement point. As a displacement gauge, various known sensors are used. For example, a contact sensor such as a dial gauge, or a noncontact sensor such as a laser sensor, a capacitance sensor, or an ultrasonic sensor can be used.
Misalignment data is calculated from a measured value of the deflection amount at each measurement point. As shown in FIG. 13, the radial deflection amount of the gas turbine rotor 1 is indicated by a fluctuation range of a distance between the outer surface 52 of the rotor disk 50 and the rotor rotation center. The rotor rotation center refers to a straight line connecting the centers of the bearing S1 and the bearing S2. From the measured value of the deflection amount on the outer surface 52 of the rotor disk 50, the center of figure O1 of a section of the rotor disk 50 to be measured is calculated, and deviation between the calculated center of figure O1 and the rotor rotation center O2 is regarded as misalignment. The misalignment thus obtained is quantitatively indicated as misalignment data including a misalignment amount and a misalignment angle.
Patent Citations 1 and 2 disclose a general method for calculating misalignment of a rotational body. Also, a method such as a least squares method is disclosed as means for calculating misalignment.